This study investigated the effects of green tea polyphenol on the serum antioxidative activity and cholesterol levels of cholesterol-fed rats and compared them with those of probucol, an antioxidant hypocholesterolemic agent. To evaluate the antioxidative activity, the susceptibility to oxidative modification of low-density lipoprotein (LDL) isolated from the serum of cholesterol-fed rats was measured, as was the serum antioxidative activity using the spontaneous autoxidation system of brain homogenate. Administration of green tea polyphenol effectively inhibited LDL oxidation and elevated serum antioxidative activity to the same degree as probucol. However, higher amounts of polyphenol than probucol needed to be administered to reduce the total, free, and LDL cholesterol levels. Furthermore, green tea polyphenol increased the levels of high-density lipoprotein (HDL) cholesterol, leading to dose-dependent improvement of the atherogenic index, an effect that was not seen with probucol. Thus, green tea polyphenol may exert an antiatherosclerotic action by virtue of its antioxidant properties and by increasing HDL cholesterol levels.
Continuous intravenous infusion of taurochenodeoxycholate at a rate of 0.4 mumol.min-1.100 gm-1 for only 30 min in rats caused threefold to tenfold greater release of proteins (alkaline phosphatase, lactate dehydrogenase and albumin) into bile in comparison with animals infused with tauroursodeoxycholate at much higher rates (1.8 mumol.min-1.100 gm-1) for 2 hr. The simultaneous infusion of tauroursodeoxycholate and taurochenodeoxycholate (0.6 and 0.4 mumol.min-1.100 gm-1, respectively) for 2 hr prevented the marked biochemical changes in the bile induced by taurochenodeoxycholate for 15 to 60 min exhibited significantly more necrotic hepatocytes, especially in zone 1, in comparison with animals infused with tauroursodeoxycholate or a combination of taurochenodeoxycholate and tauroursodeoxycholate. A good correlation was observed between biochemical and morphological indices of bile acid-induced hepatocyte injury. These data suggest that (a) primary events induced by the acute infusion of toxic bile salts responsible for cholestasis include zone 1 hepatocellular necrosis and (b) this can be prevented by the simultaneous infusion of tauroursodeoxycholate.
The effect of feeding of two different antioxidants, tetrahydrocurcumin (TC) and green tea polyphenols (PPs) on the survival of male C57BL/6 mice was examined. Mice that started to receive diets containing TC (0.2%) at the age of 13 months had significantly longer average life spans (days, mean +/- SD) than control mice (797.6 +/- 151.2 vs.882 +/- 154.6, both n = 50, controls vs. TC treated, plus 11.7%, P < 0.01). The 10% longest survival was also significantly greater in TC-treated mice (plus 6.5%, P < 0.01). In contrast, in mice that started to receive TC in their 19th month of life, no significant difference from the control mice was found for either the average life span or the 10% longest survival. In mice that received water containing PPs (80 mg/l), the average life span was also significantly longer than in the control mice (801 +/- 121.5 vs. 852.7 +/- 88.2, plus 6.4%, P < 0.05), although the 10% longest survival was not significantly different from that in the control mice (P > 0.05). The body weights of the TC (but not PP) fed mice, were slightly (2-4%) but significantly (P < 0.05) lower than the values for the corresponding ages in the control mice in the first six months of treatment. Thereafter, the difference in average body weight between the control and the TC-fed animals was totally lost. Although an additional contribution of an unintended slight decrease in food intake due to TC feeding (suspected due to the difference in body weight) is not excluded, we suggest that the feeding of nutritional antioxidants such as TC and PPs may have the potential to beneficially modify the life spans of animals.
This study investigated the antioxidative activity of green tea extract, and a green tea tannin mixture and its components, under conditions of radical generation using the hydrophilic azo compound, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) to generate peroxyl radicals at a constant and measurable rate in the cultured renal epithelial cell line, LLC-PK(1), which is susceptible to oxidative damage. Treatment with AAPH decreased cell viability and increased the formation of thiobarbituric acid-reactive substances. However, green tea extract, and the tannin mixture and its components, comprising (-)-epigallocatechin 3-O-gallate (EGCg), (-)-gallocatechin 3-O-gallate (GCg), (-)-epicatechin 3-O-gallate (ECg), (-)-epigallocatechin (EGC), (+)-gallocatechin (GC), (-)-epicatechin (EC), and (+)-catechin (C), showed protective activity against AAPH-induced cellular damage. The tannin mixture and its components exhibited higher antioxidative activity than the green tea extract. Furthermore, EGCg and GCg had higher activity than EGC and GC, respectively. In particular, EGCg exerted the most significant cellular protective activity against AAPH. These results indicate that green tea tannin may inhibit cellular loss and lipid peroxidation resulting from the peroxyl radical generated by AAPH, and that the chemical structure of tannin is also involved in the activity, suggesting that the O-dihydroxy structure in the B ring and the galloyl groups are important determinants for radical scavenging and antioxidative potential.
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